Introduction

Madagascar is well-known for its unique biological heritage (Ganzhorn et al. 2001; Goyder et al. 2017). Given its inestimable richness in ecosystems and biodiversity, it has been classified as a megadiverse country (Mittermeier 1988) and a biodiversity hotspot (Myers et al. 2000). Its long isolation from other land masses helps explain both the affinities and originality of its flora and fauna (Ganzhorn et al. 2014). Madagascar’s insularity favours its unique evolutionary history and has resulted in high endemism and explosive speciation (Mittermeier et al. 1987). However, this national biological heritage has been exposed to high levels of habitat loss from human activities, such as deforestation for agriculture, logging, mining, fire, climate change, etc. (e.g., Brown & Gurevitch 2004; Phillipson et al. 2010; Brown et al. 2015; Desbureaux & Damania 2018). To safeguard this threatened biodiversity, Madagascar committed to increase the size and number of its protected areas (Durban Vision; Gardner et al. 2018). The creation of the new Itremo Massif Protected Area (Itremo Massif PA) is a contribution by the Royal Botanic Gardens, Kew (RBG Kew) and Kew Madagascar (KM) to this commitment.

Because of its exceptional landscape and its biodiversity, the Itremo Massif had been identified by the Protected Areas System of Madagascar Commission (SAPM) as a priority conservation site. In 2008, Missouri Botanical Garden provided all the procedures necessary to obtain a temporary protection status for the Itremo Massif and from June 2010, RBG Kew undertook to take the necessary steps to implement them, achieving permanent protection for the area in 2015 (Ministère de l'Environnement, de l'Ecologie, de la Mer et des Forêts 2015).

The overall objective of the planning and management of the Itremo Massif PA is to “Conserve and maintain biodiversity in its current state to ensure the sustainability of ecological functions and improve the standard of living of the local population through sustainable and rational management of natural resources” (KMCC 2012). The Itremo Massif PA is among 853 sites worldwide recognised by the Alliance for Zero Extinction (https://zeroextinction.org/), because of the presence there of the endangered species Podocarpus capuronii de Laub.

The Itremo Massif PA, located in the Central Highlands of Madagascar (Map 1), covers an area of 24,788 ha in two blocks (Ralimanana et al. 2018) and shelters numerous plant species (Tropicos.org 2020). It is located between latitudes 20°35'40''S and 20°36'10''S, and longitudes 46°38'10''E and 46°14'35''E, 117 km west of Ivato-Ambositra, in the district of Ambatofinandrahana, part of the Amoron'i Mania region of Fianarantsoa province. To the east, it is bordered by the village of Itremo and to the west by Amborompotsy, and along with Mangataboahangy, these are the rural communities in which it lies. Its northern boundary is the Mania River and its southern boundary is delimited by the Matsiatra River.

Map 1.
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Map of the Itremo Massif Protected Area and Ambatofinandrahana Key Biodiversity Area.

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The main habitats present in the Itremo Massif PA are grasslands (70%), rocky outcrops (10.5%), tapia woodlands (6.4%), humid gallery forest (1.3%), and wetlands (0.4%) (KMCC 2012). Grassland occupies most of the land area (Nanjarisoa et al. 2017). The geology is formed by a metamorphosed sequence of shallow-water sedimentary rocks consisting of quartzite, mica schist and marble (Inzana et al. 2003), and the climate is humid and temperate in summer but cold and dry in winter (Guillaumet et al. 1975). Its geology and climate favour the establishment of different types of vegetation, as well as the high levels of endemism of its plants.

This checklist is an output of the intensive inventories undertaken by RBG Kew and KM for over two decades in the Itremo Massif PA. It is also intended to disseminate knowledge of the Itremo Massif flora to anyone who needs it, including researchers, policy makers and the broader public. Research, including taxonomic studies on the Itremo Massif flora, is continuing at pace, therefore, some taxon names will inevitably change and new species to science or to the area will likely be documented in future.

Material and Methods

Structure of the Plant Species Checklist

The checklist is derived from a database built using the data definitions, terms and data models proposed by the International Organization for Plant Information (IOPI 1993), available from https://www1.biologie.uni-hamburg.de/b-online/ibc99/iopi/iopidds2.html and follows the Taxonomic Databases Working Group Biodiversity Information Standards (Biodiversity Information Standards 2021), available from https://tdwg.github.io/rs.tdwg.org/. It was compiled using the Botanical Research and Herbarium Management System (BRAHMS v. 7; https://herbaria.plants.ox.ac.uk/bol/).

Each species entry in the Plant Species Checklist contains the following information.

Scientific Name

The names of family, genus, species and infraspecific taxa are listed alphabetically and a full list of synonyms is provided for each. Plant names and taxonomic authors follow the International Plant Names Index (IPNI, https://www.ipni.org/). Protologues are given for each name and synonym. Some names of infraspecies are not registered in IPNI and or POWO.

In general, the acceptance of species and infraspecific taxa follows the World Checklist of Vascular Plants (Govaerts et al. 2021) as implemented and updated by Plants of the World Online (POWO 2022). However, a small number of deviations are included, based on recent literature or following specialist advice.

Vernacular Names

Common or vernacular names were obtained by consultation of herbarium vouchers and from interviews during fieldtrips. The species with unknown vernacular names are marked with “Unknown”.

Geographical Distributions

Global distributions of species and taxa of lower rank are given largely following POWO (2022), as well as the Madagascan region(s) in which the taxon occurs largely following Tropicos (2020), separately and in alphabetical order. Global distributions do not include Madagascar, which is implied in all cases, for brevity. Species which only occur in Madagascar are given as endemic. Where a species is considered invasive or endemic to Itremo Massif PA or the nearby area, it is flagged as “Invasive” or “Itremo Massif PA Endemic” as appropriate at the end of its Madagascan regions list.

Elevation

Elevation represents the altitudinal range at which the species was observed or collected. It is expressed as numeric minimum and maximum elevations and measured in metres (e.g. 100 – 200 m).

Habitat and Ecology

Habitats and ecology of the species are provided in generalised narrative form, alphabetically, and are derived from the literature, herbarium vouchers, and online resources.

Phenology

Only the flowering or spore production period is provided. Species with unknown flowering or spore production periods are marked with “unknown”.

Conservation Status

The conservation status given to species and subspecies follows the IUCN categories and criteria (IUCN 2012) and was assessed following the guidelines (IUCN 2022a). The conservation status of taxa published on the IUCN Red List (IUCN 2022b) is followed by the year of publication in parentheses. Where the conservation assessment is in preparation, taxa are provided with a provisional category and criteria, where relevant, followed by the notation “NP” for not published. The conservation status for taxa which have not yet been assessed is given as “NE” for Not Evaluated following the guidelines (IUCN 2022a).

Specimens

Representative voucher specimens recorded for the taxon in the Itremo Massif PA are cited. They are provided following consultation of herbaria including K, P and TAN, herbarium acronyms according to Thiers (2023, continuously updated), and online specimen databases such as JSTOR Global Plants (https://plants.jstor.org/), the Royal Botanic Gardens, Kew, Herbarium Catalogue (https://apps.kew.org/herbcat/navigator.do), Tropicos, the Missouri Botanical Gardens’ online catalogue (https://www.tropicos.org/home) and the vascular plants catalogue of the Muséum National Histoire Naturelle (https://science.mnhn.fr/institution/mnhn/collection/p/item/search).

Results

Appendix 1, the full species checklist including summary information, is available online as a Microsoft Word document. The document is derived from a spreadsheet, which is also provided (Appendix 2).

Floristic and Physiognomic Composition

Floristic data for the Itremo Massif PA in the Catalogue of Vascular Plants of Madagascar (Tropicos.org 2020) included 565 taxa. Here, an annotated checklist of all plant species recorded in the Itremo Massif PA is produced which includes, in total, 747 accepted taxa, comprising 736 species, 1 hybrid, 3 subspecies and 7 varieties, representing 352 genera and 103 families. The checklist includes 2227 synonyms. Three plant families are represented by more than 75 species, Poaceae (111 spp.), followed by Orchidaceae (83) and Asteraceae (75) (Fig. 1A). The seven further families with more than ten species that complete the top 10 list, are Cyperaceae (63 spp.) Rubiaceae (38), Fabaceae (36), Apocynaceae (34), Lamiaceae (24), Euphorbiaceae (14) and Asphodelaceae (12). The list of top 10 genera with most species present (Fig. 1B) is led by Cyperus L. (Cyperaceae) with 32 species. The other most species-rich genera occurring in the Itremo Massif PA belong to the families: Apocynaceae (Cynanchum, 13), Asphodelaceae (Aloe, 10), Asteraceae (Helichrysum, 27; Senecio, 12), Crassulaceae (Kalanchoe, 9), Orchidaceae (Cynorkis, 15; Angraecum, 13; Eulophia, 9) and Poaceae (Eragrostis, 9; Panicum, 9).

Fig. 1.
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Most species-rich plant groups in the Itremo Massif Protected Area. A families; B genera.

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The majority of Poaceae species (63 of 111, 57%) prefer and are recorded in grassland (Nanjarisoa et al. 2017). Orchidaceae grow predominantly in humid gallery forest and tapia woodlands (47 of 83, 57%), while Asteraceae inhabit many different habitats in the Itremo Massif PA, from open grassland to more shaded tapia woodlands and humid gallery forest. The highest quality, in terms of species richness, humid gallery forest and tapia woodland can be found further away from villages, since people less frequently visit these areas. The vernacular names of most Poaceae, Orchidaceae and Cyperaceae are unknown, because local people generally are less familiar with herbaceous plants. In total, only c. 26% (68 of 257) of the species in these families have a recorded vernacular name, with orchids the lowest at 19% (16 of 83).

Distribution and Range

In this checklist, 499 taxa are endemic to Madagascar, and 70 of them are locally endemic, occurring only in Itremo Massif PA and or the surrounding area of the Central Highlands (Tables 1 and 2), of which 11 occur solely in Itremo Massif PA. Of the species which occur in or around Itremo Massif PA not endemic to Madagascar, 241 (97%) are native and 7 (c. 3%) are introduced and considered invasive (Table 1). The proportion of invasive species is, therefore, low, showing that Itremo Massif PA is not excessively threatened by human activities.

Table 1. Summary of Endemic & Endangered taxa (species and below) for the top ten most species rich families.
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Table 2. List of taxa Near Endemic (NE) or Endemic (E) to the Itremo Massif Protected Area and their conservation status.
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Threats and Extinction Risk Assessments

Among the 747 species included in the checklist, our conservation assessments (IUCN 2012) show that 216 species (29%) are threatened (Table 3), of which 10 (1%) are Critically Endangered (CR), 117 (16%) are Endangered (EN) and 89 (12%) are Vulnerable (VU). About 71% of the species are evaluated as not threatened, with 426 (57%) of Least Concern (LC), 49 (7%) Near Threatened and 4 (1%) considered Data Deficient, with a further 52 (7%) are Not Evaluated at this time. The main threats to plant diversity in the Itremo Massif PA are fires (caused unintentionally, by beekeepers, eel and crayfish catchers and camping in the PA, or intentionally by criminal gangs), artisanal mining, and Pinus L. spp. invasion.

Discussion

Plant Diversity

Our results have shown that the Itremo Massif PA has a large number of species (747), growing in different habitats such as grasslands, tapia woodlands, rocky outcrops, humid gallery forests, and wetlands (Fig. 2). Two of the most species rich plant families have been well studied in the area: the Poaceae comprising 111 species in this study, and 99 in an earlier grassland survey of the Itremo Massif PA (Nanjarisoa et al. 2017); and the Cyperaceae, comprising 63 species (Rasaminirina 2021). Taxonomic treatments at generic level have recently been published for both plant families, facilitating easier identification of grasses and sedges in Madagascar (Rabarivola et al. 2019; Rasaminirina & Larridon 2023). Compared to other inselbergs of the Central Highlands of Madagascar, such as those in the Ankaratra-Manjakatompo and Ibity Massif PAs, with 510 and 290 species, respectively (Tropicos.org 2020), the Itremo Massif PA is the richest in plant species (Fig. 3).

Fig. 2.
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A grassland; B rocky outcrops; C Tapia woodland; D humid gallery forest. photos: franck rakotonasolo.

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Fig. 3.
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Biodiversity of the Itremo Massif Protected Area. A Aerangis ellisii Schltr.; B Angraecum magdalenae Schltr. & H.Perrier; C Eulophia rutenbergiana Kraenzl.; D Begonia baronii Baker; E Beilschmiedia microphylla (Kosterm.) Kosterm.; F Tetradenia clementiana Phillipson; G Coffea buxifolia A.Chev.; H Nematostylis anthophylla Baill.; J Phyllopentas flava Razafim., Andriamih. & Kårehed; K Perrierodendron quartzitorum J.-F.Leroy, Lowry, Haev., Labat & G.E.Schatz; L Xerochlamys diospyroidea (Baill.) F.Gérard; M Xerochlamys itremoensis Hong-Wa. photos: a – l franck rakotonasolo; m andry rakotoarisoa.

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After the Poaceae (grass family), the Orchidaceae (orchid family), which is overall the most species rich plant family in Madagascar (Callmander et al. 2011), is the next best represented, with 83 species recorded from the four different, main habitats. The Orchidaceae is well studied in Madagascar, with two checklists (see Du Puy et al. 1999; Hermans et al. 2007), three field guides (see Cribb & Hermans 2009; Bosser & Lecoufle 2011; Hervouet 2018) and several publications (e.g. Hermans & Rajaovelona 2019; Hermans et al. 2021), which make the identification of orchid collections from the Itremo Massif PA relatively easy. The Asteraceae (daisy family) occupies third place in respect of species representation, with its 75 species, which are frequent in rocky outcrops, gallery forests and tapia woodlands. It is another well-studied family in Madagascar, with the 3-volume flora of Madagascar and Comoros (see Humbert 1960, 1962, 1963) and a recent publication (see Funk & Robinson 2017). The Cyperaceae (sedge family) is another of the top ten plant families in Madagascar (Larridon et al. 2021) for species diversity and is similarly well represented in Itremo Massif PA, with 63 species. The Rubiaceae (coffee family), the second most species-rich family in Madagascar (Davis & Bridson 2003; Groeninckx et al. 2010; Callmander et al. 2011), occupies fifth place in this checklist, with 38 described species. In addition, four undescribed Rubiaceae species were collected from the area: Coptosperma Hook.f. sp., two Peponidium (Baill.) Arènes spp., and Psydrax Gaertn. sp. (KM unpublished data). An as yet undescribed species of Acanthaceae was also recorded, Lasiocladus Bojer ex Nees sp. https://www.inaturalist.org/observations/36793553 (I. Darbyshire, pers. comm.). The granite, rocky outcrops in the Itremo Massif PA are suitable habitat for Aloes, with 10 species (including 2 varieties), not unlike the number of Aloe L. species known from the Ibity Massif PA (16 species, Tropicos.org 2020). All but three Aloe species in the Itremo Massif PA are threatened with extinction.

Endemicity

Itremo Massif PA is home to 499 species which are endemic to Madagascar, i.e. 67% of the species in the Itremo Massif PA are endemics and 241, 32% of its species are non-endemic, native species. This evidence supports the inclusion of the area as a Tropical Important Plant Area (TIPA) (Darbyshire et al. 2017) and or a Key Biodiversity Area (KBA, https://www.keybiodiversityareas.org/). Among the 499 endemic species, 70 are local endemics, restricted to the Itremo Massif PA, such as Tristachya betsileensis A.Camus (Vorontsova & Rakotomalala 2021), or restricted to the Itremo Massif PA and nearby areas of the Central Highlands such as Bulbostylis itremoensis Lye ex Rasam. (Rasaminirina et al. 2022). Two of the five endemic families of Madagascar occur in the Itremo Massif PA , i.e. Asteropeiaceae and Sarcolaenaceae. This valuable species richness encourages KM to promote the conservation of biodiversity with local communities in the vicinity. The low rate of non-native, introduced species (c. 3%) shows that Itremo Massif PA is not significantly frequented by local people and is little disturbed by human activities.

Threats and Conservation

The assessment of an IUCN (2012) conservation status is an important tool to prioritise plant species for conservation purposes. Repeated bush fires in the wooded grasslands, mining, and invasive plants such as Pinus spp. (Fig. 4) can threaten species that are endemic to the Itremo Massif PA and have negative impacts on their natural habitats. Further work is needed to improve our knowledge of the economic value of the species native to the Itremo Massif PA and to better understand the evolutionary processes of their habitats, to enable the development of sustainable management practices. The study of invasive species also needs to be reinforced, so that effective eradication techniques can be developed, followed by the restoration of natural habitats. Therefore, living collections held in botanic gardens such as the Botanical and Zoological Park of Tsimbazaza (PBZT) in Madagascar and seed banking (e.g. 112 species native to the Itremo Massif PA banked by the Millennium Seed Bank Partnership; http://brahmsonline.kew.org/msbp/SeedData/DW) are recommended for long-term conservation of targeted species.

Fig. 4.
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Threats to the biodiversity of the Itremo Massif Protected Area: A fire; B mining; C invasive species including Pinus spp. photos: franck rakotonasolo.

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Conclusions

The plant species checklist of the Itremo Massif PA includes 103 families and 747 species and infraspecies, with 2 families and 499 species endemic to Madagascar, 70 of which are locally endemic. The checklist provides researchers, policymakers and the broader public with baseline data for the diversity and assessment of conservation statuses of Itremo Massif PA plant species. Nearly 29% of Itremo Massif PA plant species have been assessed as threatened with extinction (1% CR, 16% EN and 12% VU). Further research into these species is required, to determine whether they are genuinely rare in every case, or sometimes under collected. The checklist of Itremo Massif PA plants, presented here, also provides a useful baseline of plant distributions, red listings, and habitats, from which an effective conservation strategy of the area and its flora can result. These results allow us, and other researchers, to identify the knowledge gaps and help us to effectively target sites for future field surveys. These data will also provide the botanical component of the identification of the site as a TIPA or KBA. The Itremo Massif PA needs a strong protection strategy to preserve its unique species. Recently, to complement the data from Itremo Massif PA and the Ambatofinandrahana KBA, the KM team has undertaken experimental studies on vegetation responses to fire and disturbance regimes, to provide a better understanding of the likely history of the different vegetation types. Tapia woodlands, humid gallery forests, grasslands and rocky outcrops are suggested to be considered as conservation targets in the Itremo Massif PA.